NEW YORK (Reuters Health) - Babies born to mothers who took antidepressants while they were pregnant had slightly slower head growth and were more likely to be born early, in a new study from the Netherlands.

Still, that doesn't prove that the drugs, called selective serotonin reuptake inhibitors (SSRIs), caused changes in the babies' development -- or that those differences would end up having long-term effects.

The findings are the latest addition to a still-complicated picture that has suggested a slightly increased risk of certain birth defects and health problems in babies of moms taking antidepressants, but also known benefits for the women.

"The accumulated data that's out there is still controversial," said Christina Chambers, who has studied the topic at the University of California, San Diego, but wasn't involved in the new work.

"It's not a simple, 'Did you take this drug or not?' You have all of these surrounding issues of the underlying condition that's being treated, how long the mother took the medication, and all of the other issues that surround it," she told Reuters Health.

In the current study, babies of mothers who were depressed but didn't take medication also had slightly slower body growth than those born to non-depressed moms.

Dr. Henning Tiemeier from Erasmus Medical Center in Rotterdam and his colleagues tracked close to 8,000 pregnant women as part of a larger study of the moms-to-be and their kids, which included ultrasounds during each trimester to assess the babies' growth.

Most of the women had few symptoms of depression, while 570 appeared depressed but weren't taking medication and another 99 were taking SSRIs.

In the womb, babies of women who were depressed, but not treated, gained less weight per week than babies of non-depressed mothers, and their heads grew a bit more slowly, too.

When moms were treated with antidepressants, however, there was no difference in their babies' body growth, but a bigger effect on head growth, which was slowed by 0.18 millimeters per week. By the time they were born, those babies' heads were about four millimeters smaller, on average, than babies of non-depressed moms.

"You could say half a centimeter... is not so big. But we think that, given that there's not a lot of variation at birth, that half a centimeter is quite substantial," Tiemeier told Reuters Health. "It's not nothing."

SSRIs are known to pass through the placenta, he said, and may reach the brain and affect its development -- although this study can't show whether that would increase the chance of kids having behavior or mental problems later in life.

Babies exposed to antidepressants were also more likely to come early: 10 percent of moms taking SSRIs had a premature birth, compared to six percent of those with untreated depression and five percent of non-depressed moms, according to findings published in the Archives of General Psychiatry.

Previous studies have suggested a slightly increased risk of some birth defects in babies of moms taking antidepressants, as well as a greater chance they will end up needing intensive care. Still, those effects have been small.

Women who are depressed and thinking about becoming pregnant should consult with their doctor about the risks and benefits of antidepressants, Tiemeier said, and consider talk therapy as another option.

"SSRIs during pregnancy may not be without risk... (but) certainly, we can't say you should not take them at this stage," he said.

Chambers agreed. "The overall picture is that this class of medications is not a huge problem in pregnancy," she said -- and the effects of not getting treatment and feeling depressed during pregnancy and with a young baby should be taken into account.

Women in the study who were taking SSRIs scored lower on the tests of depression symptoms than those with untreated depression.

"Mothers' being appropriately treated during the pregnancy is good for the baby in many respects," Chambers said.

"When the risks are low for these things and they're manageable... you weigh being the best mother you can be during pregnancy and after."